1. Field of the Invention
The present invention relates to a method of and apparatus for detecting external defects of a circular sealing member, and in particular to a method of and apparatus for detecting external defects which can be automatically and optically detected without touching thereon.
2. Description of the Prior Art
In various industrial fields, the circular members are widely used for the purpose of hermetic sealing and the like, and elastomeric materials such as rubber, plastics, etc. are selected therefor. The circular member of the type described includes a sealing portion, and the defects in this sealing portion tend to cause serious problems. In this connection, heretofore, necessity has been voiced for a system for detecting the defects in the sealing portions with high precision.
As well known, various types of seal members are used in oil or water pressure apparatuses, for example, and, particularly, the circular seal member being of a circular shape or a cup shape is provided on a piston slidable in a cylinder. The circular seal member of this type forms the most important functional part for the transmission of pressure. The sealing surface of the circular seal member, therefore, must be finished with high accuracy and be thoroughly inspected in its material quality before being disposed in the apparatus since the external defects of the circular seal member causes a pressure leakage, lowered durability, breakage and the like.
It is also well known that a rubber cup is used in the brake cylinder for use in an automobile, etc. as the circular seal member, which is such an important functional part that the depressed force applied onto the brake pedal by a driver is converted into an oil pressure force to apply a braking force to the wheels. Since the lowered quality of the cup seal of this type renders an adverse influence on braking functions of the automobile, satisfactory quality and high durability are required. Accordingly, the cup seals of the automobile, etc. must be inspected in its total number before being assembled into brake cylinders of the automobile to positively detect external defects even if the defects are very small, thus rejecting such cups as the defective ones.
The detection of defects in the circular seal member has heretofore been performed by visual inspection, and many inspectors have been required for the visual inspection of all the products of the cup seals as described above. The visual inspection also has such drawbacks that personal error and extent of fatigue of the individual inspectors tend to result in a scattering in the result of the inspection to a considerable extent, and further, that a large number of seal members cannot be automatically and effectively inspected.
A plurality of seal members such as the cup seals as described above are shaped from one rubber sheet at the same time in ordinary cases, and in the subsequent step, each cup is detached from the sheet to become a single product. In this detaching step the cutting blade is pressed against a given portion, and the roughness of the cutting blade in the cutting surface, the shifting movement of rubber sheet during cutting, etc. tend to cause flaws on the planer surface constituting a surface being finished. This planer surface does not make direct sliding contact with a brake cylinder, etc. but external defects such as surface roughening, burrs, pin holes, cracks, cuts, etc. cause considerably lowered durability of cup seal, and these external defects to extend over all the sealing portion in a short time use. The defects on such planer surface are caused by wear and damages of the cutting blade in many cases, and therefore, it is preferable that the planer surface inspection of the circular seal member is performed upon the completion of the detaching step. As seen in the conventional production, in case of inspection of the stored seal members in the final step, such a problem has been presented that it is not until a large number of defective seal members are produced that an abnormality of the cutting blade is found. Necessity has heretofore been voiced for the provision of the inspection step immediately after the finishing step. However, the above described visual inspection has presented such a disadvantage that the provision of the inspection step immediately after the detaching step has not been practicable because of the safety control for the inspectors and other factors.